Gun sight



Patented Oct. 30, 1934 UNITED STATES PATENT OFFICE GUN SIGHT James Blacklock Henderson, Blackheath, London, England Application July 26, 1919, Serial No. 313,541.

Renewed December 15, 1932. In Great Britain August 4, 1916 1 Claim.

I have led an application in England, No. 11,059, Aug. 4, 1916.

My invention consists in improvements in gunsights, the use on board ship or on other moving platforms, whereby those effects on the trajectory are compensated which are produced by the angular motion of the ship around the line of sight to the target. For example if a gun be trained fore and aft in a ship and be elevated at an angle a for range R, then if the ship rolls with amplitude 0 and the gun-sight be kept always trained on the target, the vertical plane through the axis of the gun, which is approximately the plane of the trajectory, oscillates in azimuth on both sides of the target with an amplitude tan a sin 0 and the elevation of the gun varies from to cosine 0 with double the frequency of roll. Thus at a range of 15,000 yards with a 12l gun, if the ship were rolling 10 degrees on either side of the vertical, the deflection of the shot might amount to i600 yards and the error in range might amount to -130 yards.

Various devices have been already proposed to correct this error, and serve to position the sighting line in a vertical plane parallel to the axis of the gun, and inclined at an angle relatively to the axis of the gun in this Vertical plane. In all of these prior devices, either a spirit level or a pendulum has been used to determine the horizontal or the vertical as a neecssary datum of reference, but inasmuch as both of these devices are subject to considerable disturbance due to rolling of the ship, and inasmuch as they indicate the virtual and not the true vertical, they are quite unreliable on board ship, particularly when a continuous correction is required.

According to my invention I compensate for this error by causing the line of collimation of the sighting telescope orthe like to be moved in azimuth and in elevation relatively to the ship by the angular motion around the line of sight by relative displacement of the image of the target and the cross wires or other optical parts of the telescope, the said relative displacement being effected eithgurpbyhalldgllllllafllyby awgyruoscgpnegor equivalentas the ship rolls. For a horizontal datum I use either an auxiliary line of sight which is kept laid on the horizon substantially at right angles to the main line of sight to the target, or an optical level such as one or more biprisims to view the horizon near the target, either method giving me a horizontal datum at right angles to the main line of sight. In both hand and automatically adjustable devices the line of collimation is maintained parallel to the plane of the trajectory and is depressed in that plane at a constant angle below the axis of the gun.

Figures 1 and 2 show two views of one method of applying my invention to an ordinary telescopic gun sight.

Figure 3 shows an alternative method of applying my invention to an ordinary telescope which corrects for the training error.

Figure 4 shows the device of Figures 1 and 2 65 mounted upon a gun.

In Figures 1 and 2 the telescope tube 1 (Fig. 2) is fitted with an enlarged flange 2 at the focal plane of the telescope and to this flange the eyepiece is bolted, this part not being shown in the gures. The cross-wires 3 of the telescope are attached to a ring 4 which is fixed to one end of the bar 5, the other end being provided with a handle 6. The ring 4 is mounted on a slide 7 so that it can slide parallel to the horizontal cross wire and the slide 7 is pivoted on the end of the tube 1 so that the horizontal cross wire always intersects the axis of the tube.

The length of the link 5 from the centre of the cross wires to the handle 6 is equal to the focal length of the objective of the telescope. The link 8 is pivotally attached to the bar 5 at one end by the pvot 9 and at the other end it is pivoted on a pin 10 which is adjustably mounted on an arc 11 which is part of the same casting as the ange 2. This arc is graduated in ranges or in degrees of elevation of the gun on the scale'12.

To correct the error due to the angular rolling of the ship around the line of sight to the target the bar 5 must be kept horizontal by a second observer. This can be done by keeping the sights 13 and 14 laid on the horizon or by observing the target through either of the biprisms 15 or 16 which are rigidly attached to the bar 5 by the frame 17. The biprism 15 gives two images of 95 the target one above the other when the bar 5 is horizontal and the biprism 16 gives two images side by side. Any relative displacement of these images is corrected by raising or lowering the handle 6 and by this means the bar 5 may be kept 100 horizontal.

The angle between the two bars 5 and 8 is not equal to the elevation of the gun and if the bar 5 is kept horizontal the motion of the cross wires causes the line of collimation of the telescope to 105 lie in a vertical plane parallel to the axis of the gun and depressed in that plane at a constant angle from that axis.

The manner in which the instrument of FiglllQ L and. Z may be mounted upon a gun is illus- 110 trated in Figure 4 in which the gun and the sight are shown tilted around the line of sight to simulate the effect of the rolling of the ship and the cross-sight is shown trained on the horizon at right angles to the line of sight.

The gun 53 is supported on a mounting or cradle 54 on trunnions 55, of which only one is shown. To this trunnion the sight is rigidly attached, the telescope being capable of elevation or depression relatively to the gun round a pivot 56 parallel to the gun trunnions by means of the usual Worm gearing operated by the hand-wheel 57 and having also, for purposes of applying deflection, an adjustment in azimuth about a normally vertical pivot 58 in a socket 59 which is attached to the gun trunnion. This latter deection adjustment is operated by worm gearing controlled by the hand-wheel 60.

It being assumed that the sight has been correctly directed on the target and that the angular displacement of the gun has taken place about the line of sight, the image of the target will remain in the centre of the field of view of the telescope. The movement of the cross-wires 3 brought about by operation of the handle 6 so as to keep the cross-sight 13-14 on the horizon or to maintain coincidence of the images in the biprisms 15 or 16, will therefore move the crosswres away from the image of the target seen by the observer at the telescope and his continuous action in training and laying the gun so as to counteract this relative movement of cross-wires and image will compensate the gun for the error due to tilting of the gun trunnions.

Figure 3 shows an alternative arrangement in which the observer while looking through the telescope manipulates his cross wires so as to keep them horizontal and vertical and in doing so he compensates automatically for the training error due to the rolling motion about the line of sight to the target. Figure 3 represents a section of the telescope at the focal plane. The circular sleeve 18 corresponds to the flanged portion 2 in Figure 2 and is pivoted on the telescope tube.

The cross wires are carried by a ring 19 which can slide transversely in the portion 18 on the two slides 20. One end of the slide 20 is fitted with a roller 21 which engages with a cam 22, which can be translated parallel to the axis of the telescope by a screw and nut turned by the head 23. 'I'he profile of the cam varies from section to section which engages With the roller 21 and each section is shaped so as to compensate for the error in training due to the rolling motion around the line of sight for a particular elevation of the gun, the travel of the cam being graduated in degrees of elevation of the gun or in ranges. The observer turns the sleeve 18 so as to keep his horizontal cross wire approximately parallel to the horizon, and in doing so the roller 21 engaging with the cam 22 displaces the cross wires laterally so as to compensate for the error in training due to roll. The spring 24 serves to keep the roller 21 against the cam 22.

Having now particularly described and ascertained the nature of my said invention, and in what manner the same is to be performed, I declare that what I claim is:-

In a sight for a gun mounted on an angula'rlylpo movable p latorm, a sighting devicmvable in "elevation and train and provided with a movable element having reference elements in its eld of View, an auxiliary sighting device for viewing an object lying at a substantial known angle in azimuth to the line of sight of the first named sighting device, a member connected to the auxiliary sighting device and adapted to be maintained thereby in a predetermined direction during angular movement of the platform about the line of sight of the rst named sighting device, and means connected with the member and with the element\foi;producing" relative displacementbetween vthefifmage of a distant object andthe reference elements ofthe elmetvvhby compensation may be made in elevation and train for the effect of the angular movement of the platform upon a gun mounted thereon.

JAMES BLACKLOCK HENDERSON. 

